Spatial analysis of Phellinus weirii infection centers in the central Cascades of Oregon : inferring ecological processes from patterns Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n583xz982

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  • This study was conducted to investigate why root disease centers east of the Cascade crest tend to be larger in diameter and more abundant than their counterparts to the west, within subalpine forest stands of central Oregon. The trend in a 290 km² study area appeared opposite of what was expected under the prevailing explanation for the mechanism controlling disease center distribution. The spatial distribution of detected disease, caused largely by Phellinus weirii, has been attributed to variable fire return interval. Five alternate explanations, treated as working hypotheses were investigated for directional consistency and significance. These included (1) new infection establishment rates via spore, (2) root-root spread rates of established infections, (3) the influence of barriers to spread by root contact, (4) relative fire frequency, and (5) the influence of post-fire lag time prior to resumption of root-to-root spread (recrudescence) of surviving fungal inoculum. The detected level of infection was almost three times greater east of the crest than west. Infection centers were also significantly larger in diameter and formed more extensive complexes on the east side. Establishment of new infections by spore appears very uncommon. Most sampled centers at low elevations closest to the eastern mixed conifer zone were clones, having survived one or more fires. Higher spore-initiated infection establishment rate was therefore eliminated as a plausible explanation for east-west differences. Radial spread rate of eastern infection centers was also not significantly faster than western centers. A non-significant trend was detected for Phellinus genets to be oriented parallel to the direction of topographic barriers, suggesting long-term influence of landscape barriers on movement. Trends in infection center diameter were all significant and directionally opposite of predictions derived from the fire frequency hypothesis. Recrudescence time lag of surviving fungus appears quite variable and remains a possible explanation for east-west differences, especially when interpreted within the context of differences in fire severity. Age estimates were made for 14 genets after accounting for loss of radial spread time between fires. The maximum genet age was estimated to be between 2238 - 3015 years old. The advanced age of the genets warrant an additional consideration that cause and observed effect may be out of phase in space and time.
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